Sleep disorders, which are complex, are widespread, especially in Western industrial countries, in which it is estimated that about one third of the adult population reports at least occasional difficulties with sleeping, while at least half of the sleep-disordered population have had sleep complaints for years. In U.S. Pat. No. 5,776,969 (James), which discloses a method of treating various sleep disorders, by therapy with a specified combination of chemical compounds, there is discussed and defined inter alia, primary insomnia, which may or may not be characterized by non-restorative sleep.
The definition of primary insomnia in the fourth revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) (American Psychiatric Association, 1994) states: “The predominant complaint is difficulty initiating or maintaining sleep, or non-restorative sleep, for at least one month. The sleep disturbance (or associated daytime fatigue) causes clinically significant distress or impairment in social, occupational or other important areas of functioning.” Furthermore, according to the definition, non-restorative sleep alone is sufficient to establish the diagnosis of primary insomnia, providing it results in impaired daytime functioning.
The tenth revision of the International Classification of Diseases (ICD-10) (World Health Organisation, 1991) describes nonorganic insomnia as “a condition of unsatisfactory quantity and/or quality of sleep.” It goes on to state that “there are people who suffer immensely from the poor quality of their sleep, while sleep in quantity is judged subjectively and/or objectively as within the normal limits.”
The diagnostic guidelines from ICD-10 state that the essential clinical features for a definitive diagnosis of primary insomnia are as follows: a) the complaint is either of difficulty falling asleep or maintaining sleep, or of poor quality sleep; b) the sleep disturbance has occurred at least three times per week for at least one month; c) there is preoccupation with the sleeplessness and excessive concern over its consequences at night and during the day; d) the unsatisfactory quantity and/or quality of sleep either causes marked distress or interferes with social and occupational functioning. Thus, there is repeated emphasis in ICD-10 on the equal importance of quality of sleep and quantity of sleep in the diagnosis of insomnia. The invention thus relates to primary insomnia (DSM-IV) or nonorganic insomnia (ICD-10).
Because, in normal humans, the natural hormone melatonin has an increased nocturnal concentration in the blood (according to a particular profile, see e.g. U.S. Pat. No. 5,498,423 (Zisapel)), compared with its daytime concentration, and because also a lack of nocturnal melatonin appears to correlate with the existence of sleep disorders, especially although not exclusively in the elderly, the possibility of administering exogenous melatonin to ameliorate sleep disorders has been investigated and is the subject of many scientific papers.
Thus, for example, in James, S. P., et al. (Neuropsychopharmacology 1990, 3:19-23), melatonin (1 and 5 mg) and placebo were given at 10:45 pm for one night each to 10 polysomnographically pre-screened insomniacs with a mean age of 33.4 years. These patients (who may not necessarily have had non-restorative sleep related insomnia) had quantitative sleep deficits that were demonstrable by PSG. Administration of melatonin did not alter sleep latency, sleep efficiency, total sleep time, or wake after sleep onset. The patients reported improved sleep quality, though they were not more rested in the morning and believed that their total sleep time had been shorter when on melatonin.
In Ellis, C. M., et al. (J. Sleep Res., 1996, 5: 61-65), where melatonin (5 mg) was given at 8:00 pm for 1 week to patients with psychophysiological insomnia, there was no reported change in sleep quantity or quality; 8 patients out of 15 were unable to distinguish the period of active melatonin treatment.
In Hughes, R. J., et al. (Sleep 1998, 21: 52-68), immediate release and controlled release formulations of melatonin (0.5 and 5 mg) were given 30 min before sleep and additionally, an immediate release preparation of 0.5 mg melatonin was given halfway through the night to polysomnographically prescreened elderly patients with sleep maintenance insomnia. They found that both melatonin preparations reduced sleep latency but did not alter wake time after sleep onset (an important variable in sleep maintenance insomnia) or total sleep time. No melatonin-induced changes in reported sleep quality or daytime measure of mood and alertness were found.
MacFarlane J. G., et al. (Biol Psychiatry 1991, 30(4): 371-6) have reported that melatonin (75 mg per os), administered at 10 PM daily to 13 insomniac patients for 14 consecutive days gave a significant increase in the subjective assessment of total sleep time and daytime alertness, whereas 7/13 patients reported no significant effect on subjective feelings of well-being.
Thus, there appears to be little or no evidence from published articles, that administration of exogenous melatonin (or other melatonergic agents, melatonin agonists or melatonin antagonists), in the dosages contemplated by the present invention, would be likely to improve the restorative quality of sleep in subjects affected by primary insomnia characterized by non-restorative sleep.
However, in contrast with the results of the above published papers, the present inventors have surprisingly found that melatonin (and other melatonergic agents, melatonin agonists or melatonin antagonists) in fact improves the restorative quality of sleep in subjects suffering from primary insomnia. Suitable melatonin agonists and antagonists for use in the present invention include (but are not restricted to) such compounds described in U.S. Pat. No. 5,151,446; U.S. Pat. No. 5,318,994; U.S. Pat. No. 5,385,944; U.S. Pat. No. 5,403,851; and International Patent Specification No. WO 97/00069.
The entire contents of the above-mentioned US Patents and literature references are incorporated herein by reference.